Biodiesel production from microbial lipids accumulated by oleaginous microorganisms with various carbon sources

Abstract

Renewable bioenergy has been playing an increasingly important role as a substitute for fossil fuel energy suffering from its declining supply and CO2 generation. Considering the fact that transportation fuel accounts for about 50% of the world energy consumption, the use of liquid fuel from biomass needs to be expanded substantially. Current biofuels (bioethanol and biodiesel) use edible agricultural commodities as the raw materials, which we share also as food. More biofuels production means more food price increase. Thus, in recent years much attention has been paid to the non-edible biomass for bioenergy production. The main objective of this thesis is to study a feasibility of biodiesel production from microbial lipids accumulated by oleaginous microorganisms from low-cost carbon sources of VFAs (volatile fatty acids) that could be produced with various kinds of waste biomass through anaerobic digestion. Two well-known oleaginous microorganisms, Chlorella protothecoides (Microalgae) and Cryptococcus albidus (Oleaginous yeast) were considered for the microbial lipids production with several low-cost carbon sources. Through a series of experiments and simulations the manufacturing costs of VFAs-based biodiesels were compared with respect to possible productivities in batch, fed-batch and MSC-HCDC (multi-stage continuous high cell density culture) culture systems. In batch cultures, the optimum culture temperature and pH were tested and the highest lipid content of 47.5% was obtained with urea in C. protothecoides culture. Lipid yield coefficients on VFAs were 0.138 g/g of C. protothecoides and 0.154 g/g of C. albidus, respectively. The theoretical yield coefficient was obtained closely by using VFAs as carbon source in the culture of C. albidus. In the mixture of VFAs, acetic acid showed less inhibitory effect on lipid accumulation than propionic and butyric acid. High C/N ratio in culture medium can provide higher lipid content and lipid production for bo...